[BUG] Scheduled task sessions no longer auto-prefix date in session title (regression since ~April 3, 2026)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Scheduled task sessions in Cowork used to auto-prefix the run date in the session title. This stopped working around April 3-4, 2026.
Before (working, until April 3):

"3. Apr. – Daily cofounder briefing"
"3. Apr. – Daily meeting prep"
"3. Apr. – Daily close"
"2. Apr. – Daily cofounder briefing"
"2. Apr. – Daily close"

After (broken, since April 4):

"Daily cofounder briefing"
"Daily meeting prep"
"Daily close"
"Monday weekly plan"

The date prefix was never set by the prompt or by any tool call within the session. I verified this by reading full session transcripts from before and after the change: no update_scheduled_task calls, no session rename instructions in the prompt. The platform was adding the date automatically.
Why this matters
With multiple daily scheduled tasks running every day, the session list becomes unusable without dates. Five sessions all named "Daily cofounder briefing" are indistinguishable. The date prefix was the only way to identify which run corresponds to which day.
To reproduce

Create any recurring scheduled task in Cowork (daily cadence)
Let it run for multiple days
Check session titles in the sidebar

Expected: "7. Apr. – [task description]"
Actual: "[task description]" (no date)
Environment

Claude Desktop (macOS)
Cowork mode
All scheduled tasks affected (daily, weekly, monthly)
Started between April 3 and April 4, 2026

Evidence
Session list showing the exact cutoff (oldest first):
"2. Apr. – Daily cofounder briefing" ← has date
"2. Apr. – Daily close" ← has date
"3. Apr. – Daily cofounder briefing" ← has date
"3. Apr. – Daily meeting prep" ← has date
"3. Apr. – Daily close" ← has date
--- cutoff ---
"Daily cofounder briefing" ← no date (April 4+)
"Daily meeting prep" ← no date
"Daily close" ← no date
"Monday weekly plan" ← no date

What Should Happen?

Scheduled task sessions in Cowork used to auto-prefix the run date in the session title. This stopped working around April 3-4, 2026.
Before (working, until April 3):

"3. Apr. – Daily cofounder briefing"
"3. Apr. – Daily meeting prep"
"3. Apr. – Daily close"
"2. Apr. – Daily cofounder briefing"
"2. Apr. – Daily close"

After (broken, since April 4):

"Daily cofounder briefing"
"Daily meeting prep"
"Daily close"
"Monday weekly plan"

The date prefix was never set by the prompt or by any tool call within the session. I verified this by reading full session transcripts from before and after the change: no update_scheduled_task calls, no session rename instructions in the prompt. The platform was adding the date automatically.
Why this matters
With multiple daily scheduled tasks running every day, the session list becomes unusable without dates. Five sessions all named "Daily cofounder briefing" are indistinguishable. The date prefix was the only way to identify which run corresponds to which day.
To reproduce

Create any recurring scheduled task in Cowork (daily cadence)
Let it run for multiple days
Check session titles in the sidebar

Expected: "7. Apr. – [task description]"
Actual: "[task description]" (no date)
Environment

Claude Desktop (macOS)
Cowork mode
All scheduled tasks affected (daily, weekly, monthly)
Started between April 3 and April 4, 2026

Evidence
Session list showing the exact cutoff (oldest first):
"2. Apr. – Daily cofounder briefing" ← has date
"2. Apr. – Daily close" ← has date
"3. Apr. – Daily cofounder briefing" ← has date
"3. Apr. – Daily meeting prep" ← has date
"3. Apr. – Daily close" ← has date
--- cutoff ---
"Daily cofounder briefing" ← no date (April 4+)
"Daily meeting prep" ← no date
"Daily close" ← no date
"Monday weekly plan" ← no date

Error Messages/Logs

Steps to Reproduce

1. run a scheduled task
2. look at the name of the session created.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Cowork

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_